Much that informs HIV disease and its treatment is derived from the developed world, mainly Caucasian populations. However, in many important respects HIV infection in Asia differs from other regions. The epidemiology of HIV infection is different, including large injecting drug use epidemics. Co-infection rates with hepatitis C and B are substantial. The natural history of HIV infection differs with faster progression rates and a different spectrum of opportunistic infections. There is emerging evidence that the pharmacology and toxicity of antiretroviral (ARV) treatments in Asian populations are different. Combined with differences such as ethnicities and economic development, and the coincident rapid expansion of ARV treatment access, the study of HIV disease and treatment in Asian populations is imperative. This study seeks to examine HIV disease natural history and treatment in Asia, and to assess differences with Caucasian populations. Specific studies will look at the efficacy and toxicity of ARV treatments. Studies of HIV and tuberculosis (TB), including HIV and TB treatment interactions, and immune reconstitution disease will be an important focus. The long-term effects of ARV treatments will be assessed, including trends in causes of death and comparisons with an age and behavior-matched HIV-negative group. The Asia-Pacific HIV Observational Database combines the TREAT Asia HIV Observational Database and the Australian HIV Observational Database, two established studies covering 39 sites in South, South East and East Asia and Australia, and following some 1750 individuals in Asia and 2329 in Australia. Both studies are observational, collecting demographic, treatment, disease outcome and toxicity data. A particular strength is having toxicity and outcome data collected and coded according to identical methods in Asia and Australia, allowing straightforward comparison of Asian and Caucasian populations. Both studies use an electronic transfer method of data collection that has demonstrated to be highly cost efficient while meeting stringent levels of data accuracy. Relevance: Asia (excluding China) is home to over one third of the world's population, and in 2005 some 7 million people living with HIV. It is known that in many important respects HIV epidemiology, natural history and ARV treatment outcomes differ in Asia compared with other regions. Simultaneously, ARV treatment is rapidly expanding. The Asia-Pacific HIV Observational Database aims to examine HIV disease natural history and treatment in Asia, and compare outcomes with Caucasian populations, principally in Australia, to inform optimal care and treatment for HIV disease in the region.